IIS URL Rewrite for Site Maintenance

web.config

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <system.webServer>
    <rewrite>
      <rewriteMaps>
        <rewriteMap name="MaintenanceIpAddressWhitelist" defaultValue="">
            <!-- add allowed IP addresses to grant access during maintenance period -->
            <add key="192.168.0.1" value="1" />
            <add key="127.0.0.1" value="1" />
        </rewriteMap>
      </rewriteMaps>
      <rules>
        <!-- if request is not from a white listed IP and is not for the maintenance page then redirect to maintenance page -->
        <rule name="Maintenance Redirect">
            <match url=".*" />
            <conditions logicalGrouping="MatchAll">
                <add input="{MaintenanceIpAddressWhitelist:{REMOTE_ADDR}}" matchType="Pattern" pattern="1" negate="true" />
                <add input="{REQUEST_URI}" pattern="^/maintenance.html$" negate="true" />
            </conditions>
            <action type="Redirect" url="/maintenance.html" appendQueryString="false" redirectType="Temporary"/>
        </rule>
      </rules>
    </rewrite>
  </system.webServer>
</configuration>

Thanks for the code. So userfull.